X-ray mammography is the established screening modality for breast cancer and other lesions, and also has been relied on for diagnostic and other purposes. Historically, the breast image has been recorded on x-ray film but more recently digital x-ray image receptors have come into wide use, as in the mammography system available under the trade name Selenia from the common assignee hereof, Hologic Inc. of Bedford, Mass., and from its division Lorad Corporation of Danbury, Conn. In mammography, typically a pyramid-shaped x-ray beam passes through the compressed breast and forms a two-dimensional projection image, namely, a mammogram identified herein as images M. Any one of a number of orientations can be used, such as CC (cranial-caudal) or MLO (mediolateral-oblique).
More recently, breast x-ray tomosynthesis has come into use. The common assignee has installed breast tomosynthesis systems for clinical use in this country and has sold such systems overseas. The technology typically involves taking two-dimensional (2D) projection images, identified herein as images Tp, of the immobilized breast at each of a number of angles of the x-ray beam relative to the breast. The resulting x-ray measurements are computer-processed to reconstruct images, identified herein as images Tr, of breast slices that, typically are in planes transverse to the x-ray beam axis, such as parallel to the image plane of a mammogram of the same breast, but can be at any other orientation and can represent breast slices of selected thicknesses. The range of angles is substantially less than in conventional CT (computerized tomography), i.e. substantially less than 180° plus a fan angle, e.g., a range of ±15°.
An example of a breast x-ray tomosynthesis system is the common assignee's system available under the trade name Selenia Dimensions that is sold overseas and has been installed for clinical testing in this country and includes both a tomosynthesis mode of operation and a mammogram mode of operation. See also U.S. Pat. No. 7,123,684 and U.S. patent application publications 2005/0113681 A1 and 2009/0003519 A1, U.S. Pat. Nos. 4,496,557, 5,051,904, 5,359,637, 6,289,235, 6,375,352, 6,645,520, 6,647,092, 6,882,700, 6,970,531, 6,940,943 7,356,113, 7,656,994, published U.S. Patent Applications Nos. 2004/0066904 and 2007/0263765, and Digital Clinical Reports, Tomosynthesis (GE Brochure 98-5493, November 1998). How to reconstruct tomosynthesis images is discussed in DO Grant, “Tomosynthesis: a three-dimensional imaging technique”, IEEE Trans. Biomed. Engineering, Vol BME-19, #1, (January 1972), pp 20-28. See, also, U.S. Provisional Application No. 60/628,516, filed Nov. 15, 2004, and entitled “Matching geometry generation and display of mammograms and tomosynthesis images,” and a system announced under the name Giotto Image 3D by a I.M.S. Intemazionale Medico Scintifica of Bologna, Italy. Mammography and tomography systems can also be used in interventional procedures, such as biopsy, by adding a biopsy station (for example, the system available from the common assignee under the trade name StereoLoc II Upright Stereotactic Breast Biopsy System). The patents, applications, brochures, and article cited above, as well as those cited below, are hereby incorporated by reference in this patent specification as though fully set forth herein.
X-ray breast imaging systems that can selectively take tomosynthesis projection images and conventional mammograms, such as the system available under the trade name Selenia Dimensions system, are known. They include an x-ray source and an x-ray imaging receptor that can be held in a fixed relationship to each other and moved as a unit to take conventional mammograms M, and can be decoupled from each other so that at least one can move relative to the other and to the patient's breast to take tomosynthesis projection images Tp. See also commonly assigned U.S. Pat. No. 7,583,786.
CT technology has not been widely used for x-ray imaging of the breast. In conventional CT, the patient is lying down on a gurney or platform while the x-ray source and detectors rotate about the patient. The x-ray measurements are reconstructed into images, referred herein as images CTr, of typically planar slices of the patient. The imaging planes that intersect the breast also intersect the torso and so the patient's body is unnecessarily subjected to x-radiation when only an x-ray image of the breast is of interest. In addition, the use of conventional CT for breast images can be unduly expensive. There have been proposals for CT systems that would image only the breast, without imaging the torso as well, but they require the patient to be in a prone position and also have not found wide use. See, for example, U.S. Pat. No. 3,973,126, proposing to suspend the breast of a prone patient into an opening around which an x-ray source and an x-ray detector would rotate in a horizontal plane. See also U.S. Pat. No. 6,987,831, proposing a very similar arrangement that uses more modern components. In addition, published U.S. patent publication 2010/0080343 A1 proposes a breast CT system in which the patient's breast protrudes through an opening in a vertical wall to thereby extend to the other side of the wall, where a gantry rotates an x-ray source and detector in a spiral scan motion or successive slice scan motion to image the protruding portions of the breast.
It can be desirable for a number of reasons to assess different types of x-ray images of a patient's breast. For example, over decades of reading conventional mammograms M, medical professionals have developed valuable interpretation expertise. Mammograms M may offer good visualization of micro calcifications, and may offer higher spatial resolution compared with tomosynthesis images Tp or Tr. Tomosynthesis images Tr may have different desirable characteristics—e.g., they may offer better visualization of structures that can be obscured by overlying or underlying tissue in a conventional mammogram M. CT images CTr can offer other benefits, such as the ability to obtain attenuation values for specific tissue inside the breast and to generate a three-dimensional image of volume elements (voxels) in the breast that is generally free of geometric distortions and thus can be conveniently re-processed into images of breast slices at any orientation and with any thickness. However, no system is known to the inventors herein that would make it possible to select which one or more of these three types of breast images to take with a single system, without moving the patient from one imaging system to another and perhaps from one medical facility to another.
It also can be desirable to co-register breast images taken with different x-ray modalities, e.g., so that the same real or suspected lesion can be viewed and assessed in the images from two or more modalities, as each modality may contribute different information about the lesion. While some aspects of co-registration have been provided for tomosynthesis images Tr and Tp and mammograms M (see, e.g., commonly owned U.S. Pat. Nos. 7,577,282 and 7,616,909), no co-registration is known for x-ray CT breast images, especially if taken from an upright patent, with Tr, Tp, and M x-ray images of the breast.